The present invention relates to a method for selecting an operational channel of a wireless narrow area network, a coordinator using the same, and a computer-readable recording media recording a program for realizing the method; and, more particularly, to a method for selecting an operational channel of a wireless narrow area network in which one radio channel is occupied by a plurality of coordinators at different timings by selecting a predetermined period of a radio channel where a coordinator of the wireless narrow area network is used by another coordinator as own operational channel, a coordinator using the same, and a computer-readable recording media recording a program for realizing the method.
Generally, a wireless narrow area network includes a wireless personal network, e.g., a body sensor network, a wireless sensor network, and a wireless home network. The wireless narrow area network commonly designates a wireless network whose wireless communication range is smaller than Wireless Local Area Network (WLAN).
The wireless narrow area network is widely applied to diverse instruments control by a low power wireless device and information sensing on situation and objects in a limited space such as a home, a human body and an independent observation area.
Since the wireless narrow area network can be applied to diverse application fields from now on, the wireless narrow area network is considered as core technology for supporting a future ubiquitous environment.
The wireless narrow area network basically includes one coordinator and more than one node.
There are ‘a terminal node’, which is a data generator, and ‘a router node’, which functions as a repeater for data transmission, as kinds of the nodes.
The coordinator is a center of the wireless narrow area network and has ‘network information required for forming the wireless narrow area network’ to be loaded in a beacon frame and transmitted.
The coordinator has a duty cycle operating in an active state or an inactive state in turn, i.e., a superframe including an active period and a sleep period, and an operational channel as a unique attribute. At this time, the coordinator broadcasts a beacon frame on the wireless narrow area network during the active period. In addition, the coordinator determines network identification (ID) information for identifying the wireless narrow area network node.
The network information includes network ID information determined by the coordinator, a radio channel ID number, a beacon interval (BI) and superframe duration (SD).
When the coordinator is installed at a predetermined point, the coordinator determines a radio channel to be used in own wireless narrow area network. The radio channel determined by the coordinator is different from a neighboring radio channel used in a neighboring wireless narrow area network and should be a channel where interference with the neighboring radio channel does not occur. In addition, the radio channel determined by the coordinator should provide good wireless communication between the wireless narrow area network nodes.
In particular, in case of an industrial scientific and medical (ISM) frequency band, interference between channels should be sufficiently considered since diverse wireless systems use the same channel band.
To be specific, the coordinator sequentially checks a state of each radio channel of usable channel bands in order to determine own radio channel to be used. That is, when the coordinator checks the state of the radio channel, the coordinator determines based on Received Signal Strength (RSS) whether the radio channel is occupied by the neighboring wireless narrow area network. The coordinator compares the RSS measured in a predetermined radio channel with a predetermined threshold and determines whether to use the radio channel or not.
When the RSS of the radio channel is larger than the threshold, the coordinator determines that the radio channel is occupied by another coordinator and selects another radio channel in a predetermined order or randomly.
The radio channel may be determined as a state that the radio channel is occupied by another coordinator due to interference by a signal having the same frame format or a signal having a different frame format.
When the RSS of the radio channel is lower than the threshold, the coordinator determines that the radio channel is not used by the neighboring wireless narrow area network. In this case, the coordinator may select the radio channel as a usable channel.
As described above, the coordinator checks the channel state of each radio channel of the given channel band and selects one radio channel of the checked radio channels as a private radio channel, i.e., an operational channel. That is, the coordinator exclusively selects one radio channel, which is not occupied by the coordinator of the neighboring wireless narrow area network, among the given radio channels, and determines a private radio channel.
FIG. 1 shows an operational channel selecting state in a plurality of conventional wireless narrow area networks.
As shown in FIG. 1, the radio channel selecting state in the conventional wireless narrow area networks shows a state that independent radio channels f1, f2, f3, and f4 are selected by 4 coordinators, e.g., coordinators of SAN1, SAN2 SAN3 and SAN4, existing one by one within 4 wireless narrow area networks, e.g., SAN1, SAN2 SAN3 and SAN4.
The 4 coordinators of SAN1, SAN2 SAN3 and SAN4 occupy independent radio channels such as the radio channel f1, the radio channel f2, the radio channel f3, and the radio channel f4. That is, the coordinator of SAN1 selects the radio channel f1 at a beacon interval of “32” and a superframe duration of “4”. The coordinator of SAN2 selects the radio channel f2 at a beacon interval of “64” and a superframe duration of “2”. The coordinator of SAN3 selects the radio channel f3 at a beacon interval of “16” and a superframe duration of “4”. The coordinator of SAN4 selects the radio channel f4 at a beacon interval of “64” and a superframe duration of “4”.
The conventional radio channel selection method does not have any problem when non-occupied radio channels are sufficient.
However, in the conventional radio channel selection method, the number of radio channels usable by the coordinator is limited in cases that there are a plurality of wireless narrow area networks in the same channel band, that there is a wireless network of another method such as WLAN and Ultra-WideBand (UWB) except the wireless narrow area network at the same time, and that there is a wireless network of a 2.4 GHz band where a plurality of industrial scientific and medical instruments are operated.
In particular, when the wireless narrow area network is newly installed at the area, it is difficult to provide an exclusively operated radio channel to a plurality of coordinators according to the conventional radio channel selection method.
As described above, when there are coordinators of the low duty cycle remarkably exceeding the allocation number of radio channels in a state that the number of usable radio channels is limited such as the industrial scientific and medical band, the conventional radio channel selection method has a problem in efficiently operating the radio channel of the wireless narrow area network.
Meanwhile, there is a method for scheduling a radio channel reservation and selection state of each coordinator collectively in a central master controller as another conventional method.
However, the conventional radio channel reservation and selection method cannot be applied when a plurality of wireless narrow area networks are respectively applied and operates at the same time for different services by the same or different providers in the same spatial location, i.e., when a plurality of coordinators existing in the area are controlled by different master controllers.
In order to solve the problem of the conventional technology, an efficient radio channel operation method for sufficiently providing radio channels usable by the coordinator of low duty cycle is essentially required.